1. Field of the Invention
The present invention relates to a vacuum pump with planetary gear accelerator in which a planetary gear accelerator is attached to a vacuum pump such as a rotary displacement vacuum pump (for example, a vane vacuum pump) used to operate a servo assisted brake or actuator in an automobile, for example.
2. Description of the Related Art
FIG. 8 is a cross-sectional view showing one example of a vane vacuum pump used in a servo assisted brake of an automobile, for example. In the drawing, H is a pump housing which is composed of a pump chamber part 1 and a bracket 2. An O-ring 3 is provided to seal a clearance between the pump chamber part 1 and the bracket 2, and another O-ring 4 is provided to seal off a faucet attachment (not illustrated) provided in an engine body. The reference numeral 5 designates a vane, 6 a rotor, and 7 a rotor shaft. As shown in FIG. 9, the vane 5 is installed or fitted in the rotor 6 so that it slides freely in grooves of a radial configuration. One end of the rotor shaft 7 is attached to the rotor 6 by the engagement with a spline 7a, while the other end of the same is formed so as to pass through the bracket 2 and projecting to the exterior. Bearings 8 and 9 of the rotor shaft 7 are provided so that the bearing 8 is arranged in the pump chamber part 1, while the bearing 9 is arranged in the bracket 2. The rotor 6 is arranged so that it rotates with an eccentricity of specified dimensions relative to the center of the pump chamber 1a, as shown in FIG. 9. A coupling 10 is attached by a pin 11 to the tip of the rotor shaft 7 which penetrates the bracket 2 and projects to the exterior. A bolt 12 is provided to fasten the pump chamber part 1 and the bracket 2. A retaining ring 13 is provided for positioning the bearing 9 which supports the rotor shaft 7. The pump chamber part 1 is provided with an inlet 1b and an outlet 1c. The pump chamber part 1 is further provided with a lubricator 1e which supplies engine oil for maintaining airtightness by oil among the rotor 6, the pump chamber part 1 and bracket 2; for lubricating to prevent wear among the bearing 8, the rotor 6 and rotor shaft 7; for lubricating the bearing 9; and further for lubricating, for maintaining airtightness, and for preventing wear among the vane 5, the pump chamber part 1 and the bracket 2.
Next, the operation will be explained. In this vane vacuum pump, the coupling 10 is connected to another coupling (not illustrated) of the engine side so that the rotational force is transmitted through these couplings. The rotor 6 rotates due to this rotational force, and then the vane 5 slidably fitted in the rotor 6 starts moving due to centrifugal force so as to slide along the inner circumference of the pump chamber 1a. As is common knowledge, air is sucked in from the inlet 1b due to the sliding of this vane 5, and exhaust air is discharged via the outlet 1c. By the repetition of this suction and discharge of air, negative pressure is supplied to a servo assisted brake or actuator or the like to which the inlet 1b is joined.
The performance of the above type of conventional vane vacuum pump is determined by the product of the rotational speed (rotation number per unit time) and the displacement per rotation of the vane pump. Accordingly, during low-speed rotation of the engine, there is a problem that the force of movement of the vane which is based on centrifugal force declines, and the vacuum properties weaken and become unstable. To meet the demands of large capacity vacuum performance, it is necessary to either increase the displacement per rotation, or raise the rotational number per unit of time. However, there are problems that the vane pump must be made large-sized in order to increase the displacement per rotation, and that the raising of the rotational number per unit of time is difficult because of difficulty in obtaining a required rotational speed due to limitations on the engine size. Furthermore, there is also a problem that, due to the driving conditions (installation space, rotational speed, performance requirements, etc.), the number of types of vane vacuum pumps required for every different displacement becomes large.